In a mobile communication system, a user equipment (UE) may receive information from a base station in downlink and transmit information to the base station in uplink. Information transmitted or received by a UE includes data and a variety of control information and various physical channels are used according to the type and usage of the information transmitted or received by the UE.
A downlink channel may include a downlink control channel, a downlink data channel, etc. The downlink control channel may include a control signal defining resource allocation and transmission format of a signal transmitted through the downlink data channel. Control information transmitted through the downlink control channel may be referred to as downlink control information (DCI). The downlink control channel may include a variety of DCI formats and the DCI format may include downlink resource allocation information, uplink resource allocation information, etc.
Meanwhile, a multiple-input multiple-output (MIMO) scheme is applicable in uplink or downlink. The MIMO scheme refer to a technology of utilizing two or more transmit/receive antennas in a transmitter and/or a receiver and spatially and simultaneously transmitting several data streams so as to increase system capacity. As the MIMO scheme using several transmission antennas, transmit diversity, spatial multiplexing, beamforming, etc. may be used.
If a MIMO scheme is applied to downlink transmission, in order to accurately perform downlink transmission by a downlink receiver (e.g., a UE), there is a need for DCI for downlink MIMO transmission.